Impotence is a common symptom of men with diabetes mellitus. The objective of this research proposal is to evaluate the role of three different systems in the pathophysiology of diabetic impotence. Since integrity of the autonomic nervous system is required for normal penile erections, this system will be evaluated with standard tests of vasomotor reflexes. In addition, plasma catecholamine levels will be measured as an index of adrenergic function in the resting state, during upright posture, and during the administration of pharmacologic agents which affect catecholamine release. Since penile erection also requires an adequate vascular supply, penile blood pressures will be measured. A normal male sex hormone milieu is also necessary for adequate male sexual function. Therefore, a thorough evaluation of the hypothalamic-pituitary-testicular axis will be performed in subjects participating in this study. The results of these tests should allow identification of the area of dysfunction in each patient resulting in erectile failure, thereby providing the basis for a rational approach toward therapy of this condition.